A diaphragm pump, a pump unit and an inkjet printer are provided. A housing of the diaphragm pump includes: a circular supporting groove portion for supporting a supported portion, and a passage opening for passing the supported portion to the supporting groove portion in a direction indicated by an arrow, where a shape of an outer edge of a cross section of the supported portion orthogonal to the direction indicated by an arrow is a shape of an outer edge of a circle in which a part of the outer edge is missing. A width of the passing opening at a coupling portion of the supporting groove portion and the passing opening is greater than or equal to a minimum width of the supported portion in the direction orthogonal to the direction indicated by the arrow and smaller than a maximum width of the supported portion in the relevant direction.